This invention relates to sensor assemblies for gas leak detectors, and methods of manufacturing them, and more particularly to sensor assemblies that operate on the positive-ion emission principle and utilize very low levels of sensor wattage; in the range of 500 milliwatts, for example.
In the manufacture of sensor assemblies of the type used in the halogenated gas leak detectors it has been common practice to use various types of "combs" to fill a gap between a central electrode and a surrounding heater anode of the assembly in order to space these components apart. When relatively large diameter wire is used and the heater coils of such sensors are formed to have relatively large outer diameters, a wide variety of conventional spacer combs are suitable for positioning the components in their desired operating relationships. One example of another type of prior art component spacer assembly for a gas leak detector is disclosed in U.S. Pat. No. 3,751,968--Loh, which issued on Aug. 14, 1973. The spacer shown in the Loh patent is a glass-ceramic element having a depletion layer exposed to the atmosphere that is to be sensed. Such prior art spacers are generally suitable for maintaining a desired gap between the central electrode and a surrounding heater coil, however, in devices of the size required for very low level sensor wattages, i.e., in the neighborhood of 500 milliwatts, it has been found that the sensor size must be reduced to such an extent that conventional prior art spacer arrangements such as those shown by Loh are not suitable for maintaining the thin, flexible turns of the heater coil in spaced-apart relationship.
It has also been found to be desirable to provide a convenient means for insulating the central electrode of such a sensor assembly from its surrounding heater anode coil during the assembly of these components prior to the time that a ceramic spacer element is positioned between them to maintain the desired gap. Without such an insulated central electrode, there is some risk that the central electrode may short-circuit the heater coil when it is energized during the manufacturing process.
Accordingly, it is a primary object of the present invention to provide a sensor assembly for a halogenated gas leak detector that is characterized by having a porous ceramic spacer element surrounding its central electrode and at least partially surrounding each of the turns of a heater anode to maintain these component parts in spaced-apart relationship.
Another object of the invention is to provide a sensor assembly for a gas leak detector having a coating of insulating porous ceramic material deposited on a central electrode positioned within the turns of a heater anode coil so that the central electrode cannot be shorted to the coil prior to the time that these components are fixed in spaced-apart relationship by positioning a ceramic spacer element therebetween.
A further object of the invention is to provide an improved method for manufacturing sensor elements for gas leak detectors so that reliable, relatively inexpensive sensor assemblies having a reduced sensor wattage in the range of 500 milliwatts can be consistently manufactured to high quality standards.
Additional objects and advantages of the invention will become apparent to those skilled in the art from the description presented herein when taken in connection with the accompanying drawings.